In order to form a circuit pattern on a semiconductor wafer, for example, a method of forming a circuit pattern by coating a semiconductor wafer with a coating material called a resist, placing an exposure mask (reticle) of a circuit pattern on the resist, radiating visible light, ultraviolet light, or electron beams from above, forming the circuit pattern by the resist on the semiconductor wafer by exposing the resist to light and developing the resist, and etching the semiconductor wafer using the circuit pattern of the resist as a mask has been employed.
In a semiconductor manufacturing process, when a circuit pattern is formed on various kinds of thin films formed on multiple layers, overlay accuracy between patterns of upper and lower layers is an important evaluation item of affecting the performance of a semiconductor device. As a method of evaluating an overlay between patterns of upper and lower layers, PTL 1 (JP 6-202311 A) discloses a method of acquiring an optical image of an overlay evaluation-dedicated pattern formed on a wafer in advance and evaluating a deviation amount between respective layers by image analysis.
Further, as a pattern miniaturization technique, double patterning (which is referred to as “DP”) of forming patterns on the same layer by different exposure steps and implementing high-density patterns has been put to practical use. A double exposure technique which is one of the DP techniques will be described. First, a resist is coated on a wafer to form a first resist film, and a first pattern by the first exposure is formed by exposing the first resist film to light and developing the first resist film. Then, the first pattern is frozen not to be exposed to light in second exposure. A resist for the second exposure is coated thereon to form a second resist film, and a second pattern between the first patterns is formed by the second exposure. Using this technique, a resist pattern can be formed at a pitch which is half a minimum pitch at which a resist pattern can be formed by single exposure. The DP is disclosed in PTL 2 as well.
As a method of evaluating an overlay between a first pattern and a second pattern in the DP, PTL 2 (JP 2010-177500 A) discloses a method of comparing information of the layout in which the first pattern and the second pattern to be arranged with an image obtained by imaging the patterns based on the information of the layout.